Process for recovery of c activities



Dec. 5, 1950 B. A. FRlEs- 2,532,490

PROCESS FOR RECOVERY 0F C14 ACTIVITIES Filed Sept. 28, 1948 A TToR/VEK atentec ec. 5., 195i() 2,532,490 PROCESS FOR RECOVERY OF C14 ACTIVITIES Bernard A. Fries, El Cerrito, Calif., assigner to the United States of America as represented by the United States Atomic Energy Commission Application September 2S, 1948, Serial No. 51,623

16 Claims.

This invention relates to processes for the recovery of C14 and, more particularly, to the improvements in processes for the recovery of C14 activities from irradiated metal nitrides.

The nuclear reaction represented by the equation N14(n,p)C14 has been known for some time. In the practical process for producing C14, from N14, a suitable chemical compound of nitrogen is irradiated with neutrons. Several properties are desirable in a compound which is to be so irradiated. The compound should be a stable solid, it should contain a large proportion of nitrogen, the constituents other than nitrogen should have a low capture cross section for neutrons, the compound should be free of normal carbon contamination, and the compound should be readily soluble or decomposable tc facilitate release of the C14 activities. Metallic nitrides have been found to possess these desired properties toa high degree. In carrying out the process of irradiation, metallic nitride is sealed in an aluminum container and the container containing the nitride is subsequently placed in a uranium neutron reactor. After the required period of exposure, the nitride in the sealed contaner is removed from the reactor. The C14 product activities are contained in the much larger quantity of unreacted nitride as a variety of simple carbon compounds. Older methods for recovering the C14 activities utilized an alkaline dissolution step followed by an alkaline solution-oxidation step to release the activities. This alkaline process suffers from several serious faults. These faults are that large amounts of ammonia gas are released with almost explosive violence during the reaction of the nitride with alkali and that disproportionately large amounts of oxidant are consumed in the solution-oxidation step. f Now, it has been found that the difficulties attached to the operation of the alkaline process 'may be avoided by utilizing an acidic dissolution step followed by an acidic solution-oxidation step. Furthermore, it has been found that product fractions having highly enhanced specific activity may be obtained by following certain sequences of operations in the procedures. Accordingly, it is an object of this invention to. release C14 activities from irradiated metal nitrides by reaction with acid.

It is another object of this invention to utilize acidic solution-oxidation to release C14 activities from solutions produced by the reaction of irradiated metal nitrides with acid.

It is another object of this invention to remove C14 activities, which are released by acidic reae` tion and solution-oxidation, from the reaction"` site, by entrainment in a gaseous stream.

It is a further object of this invention to recover C14 activities, which are entraned in a gaseous stream, by absorption.

It is another object of this invention to recover C14 activities which are not absorbable by subjecting the gaseously entrained activities to- The invention, both as to its organization andi, method of operation, together with further obl-,- jects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanyingu drawing, in which the single gure is a schematic illustration of apparatus suitable for carrying` out the processes of the present invention.

In accordance with the present invention, a charge of irradiated metal nitride is placed in a reaction vessel which is provided with heating and stirring means, means for introducing reagents, and means forintroducing a gaseous stream for entrainingreleased C14 activities. The reaction vessel is .followed in sequence by a stripping condenser column, a first absorber, a. combustion reactor, and a second absorber.

The nitride is then reacted with a mineral acid and heated while a slow stream of gas sweeps the system. Later a solution oxidant is added to the reaction mixture, and the boiling and sweeping is continued.

' The product may be collected as a single mass by eliminating the first absorber from the train of apparatus, but it has been found that by utilizing dual absorbers during the period of heating with acid and a fresh second absorber and no' first absorber during the period of heating which follows the addition of solution-oxi-V dant, the product may be resolved into fractions of which some possess enhanced specic activity. Now consider the materials which may be treated by this process. All metallic nitrldes are` not of equal suitability for being irradiated with neutrons. In. addition to the properties which are mentioned above as being desirable in a nitride, another extremely important property to be taken into consideration is that of re ative neutron capture cross section. It is desirable that the metallic component of the nitride have low capture cross section for neutrons. The nitrogen capture cross section for slow neutrons'is K of the order of 1.7 barns.

The limit of relative neutron capture cross section for the metallic component is of the order of tenfold this value, or for convenience, the value of approximately barns. Of course, it is the relative absorption value derived from atomic ratio and capture cross section of each component which must be employed in making the determination. A list of suitable nitrides, together with the relative capture cross section of the components, is shown in Table 1.

of 'about .fone for less `than fone. These .nitrides may f-be iconsidered to ,be :a preferred iclass.

For :the ,practical operation Of :the VAprocess, beryllium nitride was ,chosen from .the gprefherred class as a nitride which possessesaproperties that ruiniitneirradiationrequirements .This nitride was l'found to fbe entirely sari.. ...awry from the process viewpoint.

l'The reagents utilized fin the pIOC-.Qs fare as follows: .Sulfuricfaid wasfseleted asa .mineral acidfrossessine.p-ropertiesfeasilyradaptable tofutilizationvin this process. 1t l'is reguired that the acid bestronglyacidic, relatively nonvolatile, and contain no normal carbon c ontarriination.` .Several vof the other mineral acids .may be lutilized with modication'o'f the process. Y

4The solution-oxidant employedf'in this .process was ,chromium-triox'ide (Cros) and 'was .'found entirely satisfactory. The property yrequired of anoiiidant in'this. process 'isthatiitmust be capableof oxidizing carbon compounds vin solution.

The .absorbing medium utilized is i'normally'l fsodium hydroxide'solution. The 'equivalentsiof this material aretolbe found the group ofimaterals which produce Valkaline solutions "or the Ygroup which yield fr'solutions"from which insoluble carbonate 'may be precipitated.

Now with reference tothe attached 'schematic drawing'comprising'a single rigurefthere willfb'e described a suitable apparatus for conducting the operations of the processes of this invention. The apparatus may be seen to comprise a reaction vessel i, a stripping (reflux) condenser column 2, alkaline absorber 3, 'combustion reactor li, and alkaline absorber 5, connected in sequence. Reaction vessrel I is fitted with heating means 6, mechanical stirring means "i, solid reagent introducing means 8, luid reagent introducing means '9, and gas introducing means I I. Stripping condenser 2 is connected to the exit of reaction vessel I for the purpose of removing entrained aqueous and acidic components from the gaseous sweep. Absorber .3 is of the bubble type containing an absorbing medium. Absorbing 3 may be omitted from the train of apparatus by opening valve I2 and closing valves I3 and Ill. Combustion reactor i is of the normal copper oxide type used in the combustion of carbonaceous materials. Absorber f5 is similar to absorber 3. The gaseous Sweep vis vented to the atmosphere after .passage through absorber 15.

In accordance with the invention, la charge :of irradiated nitride is .placed in .reaction .vessel I. A slow stream of nitrogen .or other inert gas iis introduced to entrain the Vcarbon compoundsreleased in the reaction. A stream lof inert gas is utilized during the early zstages .of the process to eliminate hazard from explosionsof hydrogen which may be .generated ,if Aberyllium .metal is present in the nitride. l0 ml. of `,water for .each gram of nitride is then added to the nitride.,:.an.d the mixture is brought to a slow 'bioil .with yconstant stirring. 8 ml. of -18 VN 'Stili-uric `acid per gram or nitride vis now Aadded -to the boil-ing slur,- Iy. When the reaction appears complete, ,the nitro-gen sweep .is replaced by a stream of oxygen, Sufiicient acid .is added. t0 make the Solution .6

f N in HzSOi, and boiling fand sweeping .is oo ntinued for 16 :to 24 hours. At the end of that time, absorber 3 is bypassed as described above, absorber 5 Yis emptied and refilled with `fresh-absorbing medium, and the solution is .made `0.2 ,.M. ingCrO. 'Ijhe solution Vis then boiled and swept with oXygenrorva period of 16 to 24 hours. this mode of-operatiovn, three fractions of product are -collectedjthe first, in absorber vlduring 'the rst periodof gopration; ,a second, in absorber 5 during the rst period of operationyand athird, inabsorber 5, during thesecond period oi'boiling and sweeping.

The collectiono'f the various fractions fis Qmade possible Vby 'the .difference ,in chemistry of 'the .carbon compounds .found vin the soiution Whic'hlresults from .reaction of .thenlitride with acid. The compounds found .on .acidic ,dissolutionvol irradiated nitrides are C54, CQ, CO2, ,HCN Hcoon, onion, and nono. 'The criait-ICN, CH4, and COare removed from the .SQlution during the first `period of operation. The lCO2 and HCN are collece'dfin absorber :and the 'C34 and'CO are collectedi'in absorber V5y during the 'rs't period of operation. "The IjICOOH, HCHO, and CHaOI-I Vare released during fthe l second .period'jo operation bythe solution oxidation and are vco1- lected Vin absorbent. In some cases, "carriersna'r'e added tothe 4solution .toefect complete recovery. The CO2 and HCN fraction may be further-resolved by precipitating the @CO2 as carbonate Iand the HCN by means of silver. The carbonate'antl cyanide precipitatesmay-'then belburnefd and :co1- lected are separate fractions-'elf carbonate.

IAll ofthe "C14 may thus fbe collected `as car,- bonate fractions in alkaline absorbers-and 'may be removed from the y'absorbing `solution *by pre- C14 recovered from a'5.12`gm. sample of irradiated BesNz Speciiic Ac- Product as u Origin oi Fraction B2100: M1253?. of Toja/LE g' BaCOa 146. 2 2. 02)(104 2. 95)(10 431 1. 19)(104 5. 12)(10u 500. 4 9. 39 104 4. 69X107 126. 6 1. 45 105 1. 84)(107 Cleanup 1 145. 8 5. 42)(103 7. 91)(105 1NagCC), carrier was added at the time of precipitation of the BaCO.

1 NaCl carrier added.

s Carriers added.

*The cleanup consisted of material recovered by a further barium precipitation of several of the solutions remaining from recovery of the various fractions.

No original assay was made of the C11 content l of the sample so that the efliciency of recovery could not be determined. The activity of the various portions represent a total of 0.43 millicurie of C14.

Other samples of irradiated beryllium nitride were processed, for which the original C14 content was known. The results of these experiments are tabulated in the following tables:

EXAMPLE II C14 recovered from 57.95 gm. sample of irradiated BesNz sample SpecificAc- Product as 4 origin Fraction Bgloo @17122 of Togjn" g :sacos 4.14)(105 1 04)(107 3 34 103 1 33)(107 1 51)(1011 1 23)(10D 39 10s 4 35 1s Cleanup 4 57)(101 6 86x10 1lhe A CN precipitate was collected on iilter paper and the recip tate and paper were ignited together.

1 arriers added. C14 originally present millicuries 12.2 Total C recovered do 11.3 Percentage recovered per cent-.. 93

EXAIVEPLE UI C141 recovered from a 57.83 gm. sample of irradiated BeaNz Specific Ac- Product as ,4 Origin of Fraction Bianco: Q of T0515 g' Baco.

CO2 135.4 1.05Xl0 1 42 10s HC 178.2 6.31Xl0s 8 71 107 OH4-CO 1, 363. 7 1. 75 1011 2 39X10 Oxidizable 1 rst portion 890. 5 6. l8 105 5 50x10! Oxidizable 4 second portion.-. 148. 2 1.7l l05 2. 53 101 Cleanup 143. 0 3. 33X104 4. 77 X106 1 Carriers added.

1 Additional carrier added and boiling and sweeping cone tmued 24 hours.

Original Cu content of sample ..millicurles 19.7

Total C recovered 8 7 Percentage of C recoveremfaw--v Iper centw vlt will be noted from the foregoing examples that the process is capable of high eiiiciency in recovering C14. It will also be noted that the various fractions vary somewhat in the specific activity values obtained. These variations are partially explainable on the basis that BesNz as prepared may contain some normal carbon contamination in the form of free carbon, carbide, and other compounds. Further, in the processes for handling radioactive materials, it has been found desirable to add carriers to the reaction to facilitate handling. These extraneous carbon compounds will, of course, be collected along with the C14 activities. The present process does give diierentiation of fractions having enhanced speciic activity and is therefore in the nature of an improvement of the simpler mass collection process.

Operation of the present process has been proven Very successful in eliminating the diiiiculties of earlier methods. As noted above, the recovery einciency is high, the product may be obtained in highly enhanced fractions; and C14 is recovered in a stable and convenient form which may be utilized in synthesizing C14 compounds.

While it may be considered that the embodiments as disclosed are of a preferred nature, various changes may be made without departing from the invention, and it is intended to cover all such that come within the true scope and spirit of the appended claims.

What is claimed is:

1. In a method for recovering C14 activities contained in neutron irradiated metal nitrides, the step comprising reacting said neutron irradiated nitrides containing C14 activities with mineral acid, thereby releasing said activities from said nitrides.

2. The process as in claim 1, wherein said metal nitride comprises beryllium nitride and said mineral acid comprises sulfuric acid.

3. In a method for recovering C14 activities contained in neutron irradiated metal nitrides,

" the steps comprising reacting said neutron irradiated nitrides containing C14 activities with mineral acid and gaseousiy entraimng C14 activities released by said acidic reaction.

4. The process as in claim 3, wherein said metal nitride comprises beryllium nitride and said mineral acid comprises sulfuric acid.

5. In a method for recovering C14 activities contained in neutron irradiated metal nitrides, the steps comprising reacting said neutron irradiated nitrides containing C14 activities with mineral acid, gaseously entraining C14 activities released by said acid reaction, and absorbing said entrained C14 activities.

6. The process as in claim 5, wherein said metal nitride is beryllium nitride and said mineral acid is sulfuric acid.

7. In a method for recovering C14 activities contained in neutron irradiated metal nitrides, the steps comprising reacting said neutron irradiated nitrides containing C14 activities with mineral acid, gaseously entraining C14 activities released by said reaction, combusting said entrained C14 activities, and absorbing said combusted C14 activities.

8. The process as in .claim 7, wherein said metal nitride is beryllium nitride and said mineral acid is sulfuric acid.

9. In a method for recovering C14 activities contained in neutron irradiated metal nitrides, the steps comprising reacting said neutron iratacada radiated n-itrides containing C14 activities with mineral acid, adding oxidizing agent to said reacted nitrides, gaseously entraining C11activities from said acid treating and oxidizing steps, absorbing said entraned activities, combusting una absorbable activities, and absorbing said com:- busted unabsorbable activities.

10. The process as in claim 9, wherein said metal nitride is beryllium nitride and said mineral acid is sulfuric acid.

l1. .In a method for recovering C11 activities contained in neutron irradiated metal nitrides, the steps comprising reactingY said neutron ir.; radiated nitrides containing C14 activities with mineral acid, adding oxidizing agent to said reacted nitrides, gaseously entraining C11Iactivities producedby said acid reaction and oxidation,V

' contained in neutron irradiated metal nitrides,

the steps comprising: (l) reacting said neutron irradiated nitrides containing C11 activities with mineral acid, (2) oxidizing C11 activities in solution, (3) vaporizing C14 activities released by steps (1') and (2), (4) absorbing said C11 activi-l ties vaporized in step (3), (5) combusting.- C14 activities not absorbable in step (e), absorbingsaid C11 activities combusted in step (5), (7) precipitating insoluble carbonate from absorbate derived from step (6) (8) combusting C14 activities absorbed in step (4), (9) absorbing said C14 activities combusted in step (8), and (1G) precipitating insoluble carbonate from absorbate derived in step (9).

14. In a process for recovering C1L1 activities contained in neutron irradiated metal nitrides, the steps comprising: (l) reacting said neutron irradiated nitrdes containing C11 activities with mineral acid, (2) vaporizing C11 activities from the reaction-mixture ci step (i), (3) absorbingCM activities vaporized in step (2) in an alkaiine me dium, (4) combusting C14 activities unabsorbable in step (3), (5) absorbing C11 activities combusted in step (4) in an alkaline medium, (6) treating the reaction mixture remaining from step v(231'- with solution oxidant, (7) vaporizing 'Cl1 activi';.

ties released in step (6), (8) combusting said C1"1 activities vaporizedin step (7) (9) absorbing said activities combusted in step (8) in an alka' line medium, (l0) precipitating insoluble carbonate from the solution obtained in Vstep (3),

(11') precipitating insoluble cyanide from the solution reinf'iiningV from step (10) (12)r combusti'ng said insoluble cyanide obtained in step=(11) absorbing in alkaline medium the combustion productsproduced in step (12), (13) precipitating insoluble carbonate from the solution obtained in step (12), and (14) precipitating insoluble carbonate from the absorbate derived from Step 5). y,

15. 'The process as in claim 14, wherein :said metal nitride comprises beryllium nitride and wherein sulfuric acid comprises the mineral acid. employed in step (1), chromium trioxide is the.,

solution oxidant employed in step (6), and barium carbonate is the insoluble carbonate produced in steps (l0), (13) and (14).

16.-. In amethodforrecovering G11 contained in neutron irradiated beryllium nitride the steps comprising: (l) reacting said neutron irradiated beryllium nitride containing.C1-f1,v activities with` from step (6) (8) combusting the C11 compounds derived in step (4), A(9) absorbing in alkaline solution the C11 compounds combusted in step (8) and; (10) precipitating insoluble carbonates from the solution derived in step (9).

' BERNARD A. FRIES.

REFEREN CES CITED The following references are of record in the le of this patent:

Science., vol. 105, No. 2723, pp. 265-267, March` 7,1947; y y 

1. IN A METHOD FOR RECOVERING C14 ACTIVITIES CONTAINED IN NEUTRON IRRADIATED METAL NITRIDES, THE STEP COMPRISING REACTING SAID NEUTRON IRRADIATED NITRIDES CONTAINING C14 ACTIVITIES WITH MINERAL ACID, THEREBY RELEASING SAID ACTIVITIES FROM SAID NITRIDES. 